m4: Use older autoconf 2.63 compatible ax_check_compile_flag.

CentOS 6 and RHEL 6 have autoconf 2.63.

Fixes: e4b2b69e82 ("configure: Add and use AX_CHECK_COMPILE_FLAG")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

m4/ax_check_compile_flag.m4

@@ -1,5 +1,5 @@
 # ===========================================================================
-#  https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
+#   http://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -40,7 +40,7 @@
 #   Public License for more details.
 #
 #   You should have received a copy of the GNU General Public License along
-#   with this program. If not, see <https://www.gnu.org/licenses/>.
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
 #
 #   As a special exception, the respective Autoconf Macro's copyright owner
 #   gives unlimited permission to copy, distribute and modify the configure
@@ -55,10 +55,10 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 5
+#serial 3
 
 AC_DEFUN([AX_CHECK_COMPILE_FLAG],
-[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+[AC_PREREQ(2.59)dnl for _AC_LANG_PREFIX
 AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
 AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
   ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
@@ -67,7 +67,7 @@ AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
     [AS_VAR_SET(CACHEVAR,[yes])],
     [AS_VAR_SET(CACHEVAR,[no])])
   _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
-AS_VAR_IF(CACHEVAR,yes,
+AS_IF([test x"AS_VAR_GET(CACHEVAR)" = xyes],
   [m4_default([$2], :)],
   [m4_default([$3], :)])
 AS_VAR_POPDEF([CACHEVAR])dnl